NPH Insulin: Clinical Guide
NPH (Neutral Protamine Hagedorn) insulin is an intermediate-acting basal insulin indicated for glycemic control in diabetes, initiated at 10 units daily or 0.1-0.2 units/kg/day at bedtime, with systematic titration of 2 units every 3 days to reach fasting plasma glucose goals. 1
Indications
NPH insulin is used as basal insulin therapy in both type 1 and type 2 diabetes when injectable therapy is required. Consider insulin as first-line injectable when:
- A1C >10% (>86 mmol/mol) or blood glucose ≥300 mg/dL (≥16.7 mmol/L)
- Symptoms of hyperglycemia are present
- Type 1 diabetes is a diagnostic possibility 1
Special indication: NPH dosed in the morning is specifically recommended for steroid-induced hyperglycemia 1
Dosing Regimen
Initial Dosing
- Start with 10 units per day OR 0.1-0.2 units/kg per day 1
- Administer at bedtime for once-daily regimen
- Set individualized fasting plasma glucose goals
Titration Algorithm
- Increase by 2 units every 3 days to reach fasting glucose target without hypoglycemia 1
- For hypoglycemia: investigate cause; if unclear, reduce dose by 10-20% 1
- Assess adequacy at every visit
Intensification to Twice-Daily NPH
When A1C remains above goal on bedtime NPH:
- Total NPH dose = 80% of current bedtime dose 1
- Give 2/3 before breakfast, 1/3 before dinner 1
- Can add short/rapid-acting insulin (4 units or 10% of reduced NPH dose) to each injection 1
Administration Timing
Once-Daily Regimen
- Bedtime administration is standard for basal coverage 1
Twice-Daily Regimen
- Morning dose: 2/3 of total daily NPH
- Evening dose: 1/3 of total daily NPH 1
Critical Administration Detail
NPH MUST be properly resuspended before each injection. The suspension settles, requiring:
- Rotate/tip cartridge or vial up and down at least 20 times until uniformly white and cloudy 2
- For new cartridges: 10 rotations minimum 2
- Inadequate mixing (fewer than 20 times) causes dangerous dose variability ranging from 5% to 214% of intended dose 3
Common pitfall: Only 9% of patients mix adequately in real-world practice 3. Insufficient mixing is the most critical error in NPH administration and directly causes hypoglycemia and poor glycemic control.
Storage Recommendations
Unopened NPH
- Refrigerate at 36-46°F (2-8°C) 2
- Do NOT freeze; discard if frozen 2
- If refrigeration unavailable: room temperature up to 6 weeks (42 days) at ≤77°F (25°C) 2
- Keep in carton to protect from light 2
Opened/In-Use NPH
- Room temperature below 77°F (25°C) 2
- Discard after 6 weeks (42 days), even if insulin remains 2
- Vials in use should NOT be refrigerated 2
- Keep away from direct heat and light 2
Cartridges in Insulin Pens
- Unrefrigerated cartridges must be discarded 10 days after first use 2
- Store horizontally between doses at room temperature 4
Critical Safety Considerations
Hypoglycemia Risk
- NPH carries significant hypoglycemia risk compared to long-acting analogs
- Switch to basal analog if recurrent hypoglycemia develops or patient frequently forgets evening doses 1
- Hypoglycemia rates: 11% in type 1 diabetes, 5.7% in type 2 diabetes 5
Mixing Compatibility
- Can mix with rapid-acting insulins (slight absorption delay but similar postprandial response) 6
- Can mix with short-acting insulin (though not recommended unless already controlled on this mixture due to zinc binding) 6
- NEVER mix with insulin glargine (incompatible pH) 6
- Do NOT mix with lente insulins (zinc phosphate precipitation) 6
Injection Technique
- Subcutaneous injection in thighs, upper arms, buttocks, or abdomen 2
- Rotate sites approximately one inch apart 2
- Hold needle under skin for at least 6 seconds after injection 2
When to Abandon NPH
Consider switching from NPH to long-acting analog when:
- Recurrent hypoglycemia occurs 1
- Patient adherence issues with evening dosing 1
- Morning dosing would improve compliance 1
Real-world data shows: Glargine requires fewer daily injections (1.1 vs 1.9 for NPH) and lower total daily insulin doses (0.74 vs 0.76 units/kg) with similar glycemic control 5.